TECHNICAL FIELD
[0001] The present invention generally relates to medical devices for determining a measure
of hemodynamic parameters such as the cardiac output, the stroke volume, or the contractility
of a patient and in particular to implantable medical devices such a pacemaker or
cardioverter/defibrillators (ICDs) and systems including such a device and an external
programmer for determining a measure of a hemodynamic parameter such as the cardiac
output, the stroke volume, or the contractility of a patient for use, for example,
in trending heart failure or in an AV/VV optimization scheme.
BACKGROUND OF THE INVENTION
[0002] Intracardiac impedance variations has been found to reflect the cardiac function
and may hence be utilized for heart therapy in an implantable medical device such
as a heart stimulator. In particular, the cardiac impedance has been found to be of
great therapeutic value since the cardiac impedance correlates well with hemodynamic
parameters such as, for example, cardiac output and stroke volume.
[0003] Implantable medical devices of this above-mentioned general type is known. For example,
according to
U.S. 2005/0215914 the ventricular impedance is used as a measure of end-diastolic volume in order to
detect heart failure. The measured impedance, which is in inverse proportion to the
ventricular end-diastolic value, is compared with threshold values representative
of the onset and severity of heart failure and for comparison against previously detected
ventricular end-diastolic values of the patient for use in tracking the progression
of heart failure over time.
[0004] U.S. 2004/0078058 describes a heart stimulator including an analyzer that analyzes at least one predetermined
parameter of an average impedance morphology curve for use for the control of the
stimulation. A parameter having a value that is primarily dependent on the left ventricular
ejection is used. The parameter may, for example, be the integrated area below the
averaged impedance morphology curve versus time, maximum or minimum value of the average
impendance morphology curve, or the difference between the maximum and minimum value
of the average impedance morphology curve.
[0005] U.S. 5,843,137 discloses a method and apparatus for automatic determination of a pacing stimulations
threshold. Values such as maximum, minimum and direction values that characterize
the morphology of the impedance waveform is used to discriminate between capture and
loss of capture.
[0006] U.S. 6,134,472 describes an implantable heart stimulation device that measures electrical impedance
to obtain a measure of the ventricular filling. The impedance is measured at the time
when the impedance reaches a peak value, which occurs at an approximately fixed time
about 250 to 300 ms after the stimulation pulse, and immediately prior to emission
of a stimulation pulse. The difference between these two measurement values provides
a measure of the stroke volume. This procedure requires a precise synchronization
between the impedance measurements and the stimulation pulses in order to provide
a measure of the stroke volume and accordingly it may be sensitive to disturbances
and/or time delays.
[0007] EP 1 384 492 A1 discloses a heart stimulator for electric stimulation of a patient's heart that comprises
an impedance measuring unit adapted to measure the impedance (Z) between at least
two measuring electrodes intended to be implanted in a patient such that volume changes
of at least one of the chambers of the left heart result in changes in the measured
impedance. Analysing means are provided for analysing the measured impedance for the
control of the stimulation of the heart. A calculation means is provided to calculate
an average impedance morphology curve during a time interval of several cardiac cycles.
The analysing means are adapted to analyse the average impedance morphology curve
for use for the control of the stimulation to optimise the patient hemodynamics.
[0008] Thus, there is a need of an improved implantable medical device that is capable of
providing a reliable and accurate measure of hemodynamic parameters such as stroke
volume, cardiac output, or contractility.
BRIEF DESCRIPTION OF THE INVENTION
[0009] An object of the present invention is to provide an improved implantable medical
device that is capable of providing a reliable and accurate measure of hemodynamic
parameters such as stroke volume, cardiac output, or contractility.
[0010] Another object of the present invention is to provide a system including an implantable
medical device and an external programmer apparatus that is capable of providing a
reliable and accurate measure of hemodynamic parameters such as stroke volume, cardiac
output, or contractility.
[0011] A further object of the present invention is to provide an implantable medical device
and a system including an implantable medical device and an external programmer apparatus
that are capable of providing a reliable and accurate measure of hemodynamic parameters
such as stroke volume, cardiac output, or contractility for use in optimizing settings
of the implantable device, for example, pacing parameters or for deriving a condition
or change of a condition of a patient.
[0012] These and other objects are achieved according to the present invention by providing
a medical device having the features defined in the independent claim. Preferable
embodiments of the invention are characterised by the dependent claims.
[0013] According to an aspect of the present invention, there is provided an implantable
medical device including a pulse generator adapted to produce cardiac stimulating
pacing pulses, the device being connectable to at least one lead comprising electrodes
for delivering the pulses to cardiac tissue of a heart of a patient. The implantable
medical device comprises an impedance measuring unit connectable to at least two electrodes
adapted to measure cardiac impedance of the heart, the impedance measuring unit being
adapted to provide impedance information corresponding to the measured impedance;
an impedance morphology determining unit adapted to receive the impedance information
and to determine an impedance morphology curve from the impedance information; and
a calculation unit adapted to detect an extreme point section of the impedance morphology
curve and to calculate a measure of a hemodynamic parameter of the heart utilizing
the extreme point section.
[0014] According to a second aspect of the present invention, there is provided a medical
system including an external programmer apparatus comprising a communication unit
and an implantable medical device including a pulse generator adapted to produce cardiac
stimulating pacing pulses, the implantable device being connectable to at least one
lead comprising electrodes for delivering the pulses to cardiac tissue of a heart
of a patient, and a communication unit, wherein the external apparatus and the implantable
device are adapted for two-way communication of data using the communication units.
The implantable medical device further comprises an impedance measuring unit connectable
to at least two electrodes adapted to measure cardiac impedance of the heart, the
impedance measuring unit being adapted to provide impedance information corresponding
to the measured impedance. The external apparatus is adapted to obtain the impedance
information via the communication unit and further comprises an impedance morphology
determining unit adapted to receive the impedance information and to determine an
impedance morphology curve from the impedance information; and a calculation unit
adapted to detect an extreme point section of the impedance morphology curve and to
calculate a measure of a hemodynamic parameter of the heart utilizing the extreme
point section.
[0015] According to a third aspect of the present invention, there is provided a medical
system including an external programmer apparatus comprising a communication unit
and an implantable medical device including a pulse generator adapted to produce cardiac
stimulating pacing pulses, the implantable device being connectable to at least one
lead comprising electrodes for delivering the pulses to cardiac tissue of a heart
of a patient, and a communication unit, wherein the external apparatus and the implantable
device are adapted for two-way communication of data using the communication units.
The implantable medical device further comprises an impedance measuring unit connectable
to at least two electrodes adapted to measure cardiac impedance of the heart, the
impedance measuring unit being adapted to provide impedance information corresponding
to the measured impedance; and an impedance morphology determining unit adapted to
receive the impedance information and to determine an impedance morphology curve from
the impedance information. The external apparatus is adapted to obtain the impedance
morphology curve via the communication unit and further comprises a calculation unit
adapted to detect an extreme point section of the impedance morphology curve and to
calculate a measure of a hemodynamic parameter of the heart utilizing the extreme
point section.
[0016] Thus, the present invention is based on the insight that the intracardiac impedance
variations reflect the cardiac function and hence can be utilized for heart therapy
in an implantable medical device such as a heart stimulator and that the cardiac impedance
has been found to be of great therapeutic value since the cardiac impedance correlates
very well with hemodynamic parameters such as, for example, cardiac output and stroke
volume. In particular, the actual shape of the cardiac impedance signal and the morphology
of the peak section and its immediate surroundings has been found to contain valuable
information regarding the hemodynamic performance of a patient. This information is,
according to the present invention, used to determine or calculate a measure of a
hemodynamic parameter of the patient, for example, cardiac output, stroke volume,
or contractility. This measure may, in turn, be used to control heart stimulation
to optimize hemodynamics or to trend, for example, the development of heart failure.
[0017] According to the second aspect of the present invention, the programmer obtains impedance
data from the implantable device and performs the impedance morphology determination
and the calculation of the hemodynamic measure. That is, the impedance data processing
is mainly performed in the programmer and thus the data processing executed in the
implantable device can be minimized. The impedance data transfer to the programmer
may be performed continuously or at regular intervals.
[0018] According to the third aspect of the present invention, the programmer obtains impedance
curves from the implantable device and performs the calculation of the hemodynamic
measure. That is, the calculation of the hemodynamic measure is performed in the programmer
and thus the data processing executed in the implantable device can be reduced. The
transfer of impedance curves to the programmer may be performed continuously or at
regular intervals.
[0019] In one embodiment of the present invention, the implantable medical device includes
an analyzer adapted to analyze the measure to optimize at least one pacing parameter
of the pulse generator or to derive a change of a condition of the patient. Thereby,
the heart stimulation pulses may be controlled such that the patient hemodynamics
is optimized. For example, an AV/VV interval may be optimized. The obtained measure
can also be used to trend conditions such as, for example, heart failure. In an alternative
embodiment, the analyzer is arranged in the external programmer apparatus.
[0020] According another embodiment of the present invention, the calculation unit is adapted
to calculate the measure by means of the shape of the impedance morphology curve in
a time window surrounding the peak section of the impedance morphology curve.
[0021] In a further embodiment of the present invention, the impedance morphology determining
unit is adapted to determine an averaged impedance morphology curve from the impedance
information during a time interval of a plurality of cardiac cycles of the heart.
For example, a predetermined number of consecutive heart beats may be used to create
the averaged impedance curve. In an alternative embodiment, the impedance morphology
determining unit is adapted to perform a filtering procedure of the received impedance
information and to determine an impedance morphology curve from the filtered impedance
information.
[0022] In another embodiment of the present invention, the calculation unit is adapted to
detect the maximum value of the impedance morphology curve and to centre the time
window about the value. The maximum value or peak section of the curve may be located
by using the first and second time derivatives of the curve section.
[0023] In yet another embodiment of the present invention, the calculation unit is adapted
to fit a polynomial of degree two to the section of the impedance morphology curve
in the time window.
[0024] According to further embodiment of the present invention, a curvature component of
the polynomial is used as the measure. The second degree constant has been found to
contain information of the magnitude of the curvature of the cardiac impedance waveform
and may thus be used as the measure of the shape of the cardiac impedance signal,
and, in turn, as a measure of the hemodynamic parameter, for example, the stroke volume
or the cardiac output.
[0025] In another embodiment of the procedure for calculating the measure according to the
present invention, the sample corresponding to the maximum value is identified, a
window centred about the maximum value containing a predetermined number of samples
is defined, the values of the start and end samples of the window, respectively, are
identified, an average value of the start and end values is calculated, and a ratio
of the average value and the maximum value is calculated as the measure. According
to an alternative, a window centred about the maximum value having a predetermined
length of time is defined and the samples corresponding to the start and end of the
time window are identified and used to calculate the ratio.
[0026] Alternatively, to calculate the measure of the hemodynamic parameter, the sample
corresponding to the maximum value is identified, a window centred about the maximum
value containing a predetermined number of samples is defined, and an area of the
window by adding the values of the predetermined number of samples is calculated as
the measure. According to an alternative, a window centred about the maximum value
having a predetermined length of time is defined and the values of the samples included
in the time window are added up to calculate the area.
[0027] In a further embodiment of the procedure for calculating the measure in accordance
with the present invention, the sample corresponding to the maximum value is identified,
a time window centred about the maximum value containing a predetermined number of
samples is defined, the values of the start and end values of the window, respectively,
are identified, a first average slope from the sample corresponding to the start value
to the sample corresponding to the maximum value is calculated, a second average slope
from the sample corresponding to the maximum value to the sample corresponding to
the end value is calculated, and the first slope and the second slope is used to calculate
the measure. For example, a ratio between the slopes or a product of the slopes can
be calculated.
[0028] In yet another embodiment of the present invention, a time window is defined at a
predetermined amplitude in relation to the maximum value and a width of the time window
as the measure is calculated.
[0029] In one embodiment, the resistive part of the cardiac impedance is used. Furthermore,
the impedance information may also or alternatively, for example, include the magnitude
of the complex impedance, the real and/or imaginary part (i.e. the inductive or capacitive
part) of the complex impedance.
[0030] According to further embodiments, the hemodynamic parameter is stroke volume, cardiac
output, or contractility.
[0031] The features that characterize the invention will be better understood from the following
description used in conjunction with the accompanying drawings. It is to be expressly
understood that the drawings is for the purpose of illustration and description and
is not intended as a definition of the limits of the invention. These and other objects
attained, and advantages offered, by the present invention will become more fully
apparent as the description that now follows is read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] In the following detailed description, reference will be made to the accompanying
drawings, of which:
Fig. 1 is block diagram of the primary functional components of an embodiment of the
implantable medical device according to the present invention.
Fig. 2 is a block diagram of a part of the embodiment of the implantable medical device
shown in Fig. 1.
Fig. 3 is a general block diagram of an embodiment of the system according to the
present invention.
Fig. 4 is block diagram of the primary functional components of an embodiment of the
implantable medical device of the system shown in Fig. 4 according to the present
invention.
Fig. 5 is a general block diagram of another embodiment of the system according to
the present invention.
Fig. 6 is block diagram of the primary functional components of an embodiment of the
implantable medical device of the system shown in Fig. 5 according to the present
invention.
Fig. 7 is a flow chart illustrating steps for determining a measure of a hemodynamic
parameter.
Fig. 8 is a flow chart of a calculation procedure
Fig. 9 is a flow chart of another calculation procedure
Fig. 10 is a flow chart of yet another calculation procedure.
Fig. 11 is a flow chart of a further calculation procedure
DETAILED DESCRIPTION OF THE INVENTION
[0033] With reference first to Fig. 1, an embodiment of the implantable medical device according
to the present invention will be shown. This embodiment of the present invention is
implemented in the context of a pacemaker 20 implanted in a patient (not shown). The
pacemaker 20 comprises a housing being hermetically sealed and biologically inert.
Normally, the housing is conductive and may, thus, serve as an electrode. One or more
pacemaker leads, where only two are shown in Fig. 1, 2 6a and 2 6b, are electrically
coupled to the pacemaker 20 in a conventional manner. The leads 26a, 26b extend into
the heart (not shown) via a vein of the patient. One or more conductive electrodes
for receiving electrical cardiac signals and/or for delivering electrical pacing to
the heart are arranged near the distal ends of the leads 26a, 26b. As the skilled
man in the art realizes, the leads 26a, 26b may be implanted with its distal end located
in either the atrium or ventricle of the heart.
[0034] The leads 26a, 26b may be unipolar or bipolar, and may include any of the passive
or active fixation means known in the art for fixation of the lead to the cardiac
tissue. For example, a good fixation of electrodes can be obtained by means of a screw-in
electrodes. Alternatively, the lead distal tip (not shown) may include a tined tip
or a fixation helix.
[0035] The leads 26a, 26b comprises one or more electrodes, such a tip electrode or a ring
electrode, arranged to, inter alia, transmit pacing pulses for causing depolarization
of cardiac tissue adjacent to the electrode(-s) generated by a pace pulse generator
22 under influence of a control circuit 23 comprising a microprocessor. The control
circuit 23 controls, inter alia, pace pulse parameters such as output voltage and
pulse duration. A memory circuit 31 is connected to the control circuit 27, which
memory circuit 35 may include a random access memory (RAM) and/or a non-volatile memory
such as a read-only memory (ROM). Detected signals from the patients heart are processed
in an input circuit 33 and are forwarded to the microprocessor of the control circuit
27 for use in logic timing determination in known manner.
[0036] Furthermore, an impedance measuring unit 25 is adapted to carry out impedance measurements
of the cardiac impedance of the patient. The impedance vector used should preferably
capture the filling and emptying of the ventricle (right or left). The impedance measuring
unit 25 is thus arranged to apply excitation current pulses between a first electrode
and a second electrode arranged to positioned, for example, within a heart of the
patient. In one embodiment which does not for part of the invention, the current is
emitted between a right ventricular tip electrode and a left ventricular tip electrode.
The first and second electrode may also be positioned outside the heart. The impedance
measuring unit 25 is also arranged to measure the voltage between a third and fourth
electrode arranged, for example, at a lead 26a, or 26b. The third and fourth electrode
are arranged such that they can be located within the heart of the patient, for example,
in a vein/artery of the heart. In one embodiment which does not form part of the invention,
the voltage is sensed between a right ventricular ring electrode and a left ventricular
ring electrode.
[0037] According to another embodiment which does not form part of the invention, tri-polar
measurements are used to perform the impedance measurements where the current is sent
out between an RV-tip (i.e. the distal electrode in a bipolar lead located in right
ventricle) and an RV-coil (i.e. the conductor in a bipolar lead having a helical configuration
located in the right ventricle) and the voltage is measured between an RV-ring (i.e.
the proximal electrode in a bipolar lead located in right ventricle) and the RV-coil.
[0038] The impedance measuring unit 25 may comprise an amplifier (not shown) that amplifies
the evoked voltage response, i.e. the measured voltage, and may be synchronized in
a multiplier with the excitation current. Thus, the impedance measuring unit 25 obtains
the cardiac impedance given by the delivered current and the evoked voltage response.
Then, the impedance information corresponding to the measured impedance is sent to
an impedance processing unit 21.
[0039] The impedance information used may include the resistive part of the cardiac impedance.
Furthermore, the impedance information may also or alternatively, for example, include
the magnitude of the complex impedance, the real and/or imaginary part (i.e. the inductive
or capacitive part) of the complex impedance.
[0040] The impedance processing unit 21 may be adapted to determine an averaged impedance
morphology curve from the received impedance information during a time interval of
a plurality of cardiac cycles. In another embodiment, the received impedance information
is filtered and a morphology curve based on the impedance information obtained during
one heart beat is determined. The signals may be bandpass filtered to remove the DC-component.
Furthermore, an extreme point section of the impedance morphology curve is detected
and a measure of a hemodynamic parameter of the heart, for example, stroke volume,
cardiac output, or contractility, utilizing the extreme point section is calculated.
In one embodiment, the extreme point section is a peak section. Different approaches
for calculating the measure will be discussed below. Thereafter, the obtained measure
is analyzed to optimize at least one pacing parameter of the pulse generator or to
derive a change of a condition of the patient. The control circuit 23 may be connected
to the impedance processing unit 21 to control the heart stimulation pulse generator
22 in response to the output from the impedance processing unit 21 such that the patient
hemodynamics can be optimized. For example, an AV/VV interval may be optimized. The
obtained measure can also be used to trend, for example, heart failure.
[0041] With reference to Fig. 2, an embodiment of the impedance processing unit 21 will
be described. An impedance morphology determining unit 27 is adapted to receive the
impedance information corresponding to the measured impedance from the impedance measuring
unit 25. The impedance morphology determining unit 27 may be adapted to determine
an averaged impedance morphology curve from the received impedance information during
a time interval of a plurality of cardiac cycles. In another embodiment, the received
impedance information is median filtered and a morphology curve based on the impedance
signal obtained during one heart beat is determined.
[0042] In a calculation unit 29, an extreme point section of the impedance morphology curve
is detected and a measure of a hemodynamic parameter of the heart, for example, stroke
volume, cardiac output, or contractility, utilizing the extreme point section is calculated.
In one embodiment, the extreme point section is a peak section. The measure obtained
from the calculation unit 29 is analyzed in an analyzer 31 to optimize at least one
pacing parameter of the pulse generator or to derive a change of a condition of the
patient. The control circuit 23 may be connected to the analyzer 31 for the optimization
discussed above.
[0043] The implantable medical device 20 is powered by a battery (not shown), which supplies
electrical power to all electrical active components of the medical device 20. Data
contained in, for example, the memory circuit 35 can be transferred to a programmer
(not shown in Fig. 1) via a communication unit 37, e.g. a telemetry unit, including
a programmer interface for use in analyzing system conditions, patient information,
etc. The analyzer 31 may also transfer data to the programmer via the communication
unit 37.
[0044] With reference now to Figs..3-6, embodiments of the system according to the present
invention will be discussed. Like or similar parts in Fig. 1, 2, 4 and 6 are denoted
with the same reference numerals and therefore the description of such parts will
omitted since they were discussed above with respect to Figs. 1 and 2. Likewise, like
or similar parts in Fig. 3 and 5 are denoted with the same reference numerals and
therefore the description of such parts will omitted since they were discussed above
with respect to Fig. 3.
[0045] With reference first to Fig. 3 and 4, one embodiment of the system according to the
present invention will be described. In Fig. 3, it can be seen that the system 50
includes an implantable medical device 40, which is shown in more detail in Fig. 4,
and an external programmer apparatus 51. The implantable device 40 and the external
programmer 51 are adapted for two-way communication of data between each other via
communication units 37 and 53, respectively. In this embodiment, the implantable medical
device 40 comprises the impedance morphology determining unit 27 adapted to receive
the impedance information from the impedance measuring unit 25 and to determine an
impedance morphology curve from the impedance information. The impedance morphology
curves can be stored in the memory circuit 37 or they may be buffered locally in the
impedance morphology determining unit 27 before being transferred to the external
programmer apparatus 51 via the communication units 37 and 53, respectively. This
data transfer can be performed either continuously or at predetermined intervals of
time. In the external programmer apparatus 51, the received impedance morphology data
is processed in a calculation unit 55 to detect an extreme point section of the impedance
morphology curve (or extreme points sections of respective curves) and a measure of
a hemodynamic parameter of the heart, for example, stroke volume, cardiac output,
or contractility, utilizing the extreme point section is calculated using the extreme
point section. In one embodiment, the extreme point section is a peak section. The
measure obtained from the calculation unit 55 may be analyzed in an analyzer 57 to
optimize at least one pacing parameter of the pulse generator of the implantable medical
device 40 or to derive a change of a condition of the patient. The updated pacing
parameters may be communicated to the implantable medical device 40 via the communication
units 53 and 37, respectively, to control the heart stimulation pulse generator 22
in response to the output from the impedance processing unit 57 such that the patient
hemodynamics can be optimized. For example, an AV/VV interval may be optimized. The
obtained measure can also be used to trend, for example, heart failure.
[0046] With reference first to Fig. 5 and 6, another embodiment of the system according
to the present invention will be described. In Fig. 5, it can be seen that the system
70 includes an implantable medical device 60, which is shown in more detail in Fig.
6, and an external programmer apparatus 71. The implantable device 60 and the external
programmer 71 are adapted for two-way communication of data between each other via
communication units 37 and 53, respectively. In this embodiment, the impedance information
data from the impedance measuring unit 25 is streamed to the external programmer apparatus
71. Alternatively, the impedance information data can be stored in the memory circuit
37 or buffered locally in the impedance measuring unit 25 before being transferred
to the external programmer apparatus 71 via the communication units 37 and 53, respectively.
This data transfer can be performed at predetermined intervals of time. In the external
programmer apparatus 71, the received impedance data is processed in a impedance morphology
determination unit 54 to determine an averaged impedance morphology curve from the
received impedance information during a time interval of a plurality of cardiac cycles.
In another embodiment, the received impedance information filtered and a morphology
curve based on the impedance signal obtained during one heart beat is determined.
In the calculation unit 55 an extreme point section of the impedance morphology curve
(or extreme points sections of respective curves) and a measure of a hemodynamic parameter
of the heart, for example, stroke volume, cardiac output, or contractility, utilizing
the extreme point section is calculated using the extreme point section. In one embodiment,
the extreme point section is a peak section. The measure obtained from the calculation
unit 55 may be analyzed in an analyzer 57 to optimize at least one pacing parameter
of the pulse generator of the implantable medical device 60 or to derive a change
of a condition of the patient. The updated pacing parameters may be communicated to
the implantable medical device 60 via the communication units 53 and 37, respectively,
to control the heart stimulation pulse generator 22 in response to the output from
the impedance processing unit 57 such that the patient hemodynamics can be optimized.
For example, an AV/VV interval may be optimized. The obtained measure can also be
used to trend, for example, heart failure.
[0047] Turning now to Fig. 7, a general description of a method for calculating the measure
of a hemodynamic parameter will be given. First, at step 100, it may be checked whether
at least one predetermined measurement criteria is fulfilled.
[0048] However, this step is optional. At step 102, impedance measurements of the cardiac
impedance of the patient is performed. If the criteria check step is performed, the
measurement step 102 is performed if the predetermined criteria is fulfilled. Thereafter,
at step 104, an averaged impedance morphology curve from the received impedance information
during a time interval of a plurality of cardiac cycles is determined. In another
method, the received impedance information is filtered and a morphology curve based
on the impedance signal obtain during one heart beat is determined. As discussed above,
this step may be performed either in the implantable medical device or in the external
programmer apparatus. If the morphology curves are calculated in the programmer, the
impedance data may streamed over to the prgrammer from the implantable device or is
may be transferred at regular intervals. If the curves are calculated in the implantable
device, the curves may be transferred on a continuos basis or at regular intervals.
Then, at step 106, an extreme point section of the impedance morphology curve is detected.
In one embodiment, the extreme point section is a peak section. A measure of a hemodynamic
parameter of the heart, for example, stroke volume, cardiac output, or contractility,
utilizing the extreme point section is calculated. Different approaches for calculating
the measure will be discussed below. The calculation step may be executed in the programmer
or in the implantable device.
[0049] Thereafter, at step 108, the obtained measure may be analyzed to optimize at least
one pacing parameter of the pulse generator or to derive a change of a condition of
the patient. The control circuit 23 may receive the updated pacing parameters to control
the heart stimulation pulse generator 22 in response to the output from the such that
the patient hemodynamics can be optimized. For example, an AV/VV interval may be optimized.
The obtained measure can also be used to trend, for example, heart failure.
[0050] Referring now to Figs. 8-12, different calculations procedures for calculating the
measure of a hemodynamic parameter of the heart, for example, stroke volume, cardiac
output, or contractility according to the present invention will be described. As
discussed above, the actual shape of the cardiac impedance signal and especially the
morphology of the extreme points sections, e.g. the peak point section, and the immediate
surroundings contain information of the hemodynamic status of the patient that can
be used to obtain the above-mentioned relative measure of the hemodynamic parameter.
[0051] With reference first to Fig. 8, a first calculation procedure will be disscussed.
First, at step 120, an extreme point of the impedance morphology curve is detected.
In this procedure, a top part or peak value of the impedance morhology curve is detected
and time window having a predetermined length is centered about this peak value. To
locate the peak section of the curve, minima and maxima in the first and second time
derivative of the curve can be used. Thereafter, at step 122, a polynomial of a predetermined
degree, e.g. a 2
nd degree polynomial, is adapted to the curve section of the predetermined time window.
If the 2
nd degree polynomial is used, it will hence be the following form:
a·x2+b·x+c. Then, at step 124, the constant a is stored as a measure of the curvature of the
waveform peak and is used as a measure of the hemodynamic parameter.
[0052] Turning instead to Fig. 9, another calculation procedure will be disscussed. First,
at step 130, an extreme point of the impedance morphology curve is detected. In this
procedure, a top part or peak value of the impedance morhology curve is detected and
time window having a predetermined length is centered about this peak value. Then,
at step 132, the sample,
Sn, corresponding to the maximum value or peak value is identified. Subsequently, at
step 134, a window consiting of samples
Sn-m to
Sn+m centred about the maximum value containing a predetermined number 2m+1 of samples,
wherein m may be a number between 5 and 35 with
fs=128Hz (corresponding to 40-280 mS). Thereafter, at step 136, the values of the start
and end points or samples of the window, respectively, are identified and an average
value of the start and end values are calculated in accordance with:
[0053] Then, at step 138, a measure of the hemodynamic parameter is calculated as a ratio
of the average value and the maximum value β in accordance with:
[0054] With reference now to Fig. 10, a further calculation procedure will be disscussed.
First, at step 140, an extreme point of the impedance morphology curve is detected.
In this procedure, a top part or peak value of the impedance morhology curve is detected
and a time window having a predetermined length is centered about this peak value.
Then, at step 142, the sample,
Sn, corresponding to the maximum value or peak value is identified. Subsequently, at
step 144, a window consiting of samples
Sn-m to
Sn+m centred about the maximum value containing a predetermined number 2m+1 of samples,
wherein m may be a number between 5 and 35 with
fs=128Hz (corresponding to 40-280 mS). Thereafter, at step 146, the area of the defined
curve section is estimated by adding up sample values for the samples
Sn-m to
Sn+m. This can be performed with or without time- or amplitude normalization. Finally,
at step 148, the calculated area is used a the measure of the hemodynamic parameter,
for example, cardiac output or stroke volume.
[0055] Turning to Fig. 11, yet another procedure will be disscussed. First, at step 150,
an extreme point of the impedance morphology curve is detected. In this procedure,
a top part or peak value of the impedance morhology curve is detected and time window
having a predetermined length is centered about this peak value. Then, at step 152,
the sample,
Sn, corresponding to the maximum value or peak value is identified. Subsequently, at
step 154, a window consiting of samples
Sn-m to
Sn+m centred about the maximum value containing a predetermined number 2m+1 of samples,
wherein m may be a number between 5 and 35 with
fs=128Hz (corresponding to 40-280 mS). Thereafter, at step 156, the average slopes from
sample
Sn-m to the maximum point, A, and from the maximum point to the sample
Sn+m, B, are calculated, respectively. Finally, at step 158, the measure is calculated
as the ratio between the slopes in accordance with the following:
[0056] This ratio thus describes a warpedness of the section of the curve of the window.
[0057] Alternatively, the measure can be calculated as:
[0058] According to a further alternative, the measure is calculated as:
[0059] According to still another procedure, a time window at a predetermined amplitude
in relation to the maximum value is defined and a width of the time window is calculated
as the measure.
[0060] It is to be understood that the above description of the invention and the accompanying
drawings is to be regarded as a non-limiting example thereof and that the scope of
protection is defined by the appended patent claims.
1. An implantable medical device including a pulse generator adapted to produce cardiac
stimulating pacing pulses, said device being connectable to at least one lead comprising
electrodes for delivering said pulses to cardiac tissue of a heart of a patient, comprising:
an impedance measuring unit connectable to at least two electrodes adapted to measure
cardiac impedance of said heart, said impedance measuring unit being adapted to provide
impedance information corresponding to said measured impedance;
an impedance morphology determining unit adapted to receive said impedance information
and to determine an impedance morphology curve from said impedance information; characterized in that said medical device comprises
a calculation unit adapted to detect an extreme point section of said impedance morphology
curve and to calculate a measure of a hemodynamic parameter of said heart utilizing
said an extreme point section.
2. The implantable medical device according to claim 1, wherein said extreme point section
is a peak section.
3. The implantable medical device according to claim 1 or 2, further comprising an analyzer
adapted to analyze said measure to optimize at least one pacing parameter of said
pulse generator or to derive a change of a condition of said patient.
4. The implantable medical device according to claim 2 or 3, wherein said calculation
unit is adapted to calculate said measure by means of the shape of the impedance morphology
curve in a time window surrounding said peak section of said impedance morphology
curve.
5. The implantable medical device according to any one of preceding claims, wherein said
impedance morphology determining unit is adapted to determine an averaged impedance
morphology curve from said impedance information during a time interval of a plurality
of cardiac cycles of said heart.
6. The implantable medical device according to any one of claims 1-4, wherein said impedance
morphology determining unit is adapted to perform a filtering procedure of said received
impedance information and to determine an impedance morphology curve from said filtered
impedance information.
7. The implantable medical device according to any one of preceding claims, wherein said
calculation unit is adapted to detect the maximum value of said impedance morphology
curve and to centre said time window about said value.
8. The implantable medical device according to any one of preceding claims, wherein said
calculation unit is adapted to fit a polynomial of degree two to the section of the
impedance morphology curve in said time window.
9. The implantable medical device according to claim 8, wherein said calculation unit
is adapted to calculate a curvature component of said polynomial as said measure.
10. The implantable medical device according to claim 7, wherein said calculation unit
is adapted to:
identify the sample corresponding to the maximum value;
define a window centred about the maximum value containing a predetermined number
of samples;
identify the values of the start and end samples of said window, respectively;
calculate an average value of said start and end values; and
calculate a ratio of said average value and said maximum value as said measure.
11. The implantable medical device according to claim 7, wherein said calculation unit
is adapted to
identify the sample corresponding to the maximum value;
define a window centred about the maximum value containing a predetermined number
of samples; and
calculating an area of said window by adding the values of said predetermined number
of samples as said measure.
12. The implantable medical device according to claim 7, wherein said calculation unit
is adapted to
identify the sample corresponding to the maximum value;
define a time window centred about the maximum value containing a predetermined number
of samples;
identify the values of the start and end values of said window, respectively;
calculate a first average slope from the sample corresponding to said start value
to said sample corresponding to said maximum value;
calculate a second average slope from the sample corresponding to the maximum value
to the sample corresponding to the end value; and
calculate a ratio between said first slope and said second slope as said measure.
13. The implantable medica device according to claim 7, wherein said calculation unit
is adapted to
define a time window at a predetermined amplitude in relation to the maximum value;
and
calculating a width of said time window as said measure.
14. The implantable medical device according to any one of preceding claims, wherein said
hemodynamic parameter is stroke volume, cardiac output, or contractility.
15. A medical system including an external programmer apparatus comprising a communication
unit and an implantable medical device including a pulse generator adapted to produce
cardiac stimulating pacing pulses, said implantable device being connectable to at
least one lead comprising electrodes for delivering said pulses to cardiac tissue
of a heart of a patient, and a communication unit, said external apparatus and said
implantable device being adapted for two-way communication of data using said communication
units,
wherein said implantable medical device further comprises an impedance measuring unit
connectable to at least two electrodes adapted to measure cardiac impedance of said
heart, said impedance measuring unit being adapted to provide impedance information
corresponding to said measured impedance; and
wherein said external apparatus is adapted to obtain said impedance information via
said communication unit and further comprises
an impedance morphology determining unit adapted to receive said impedance information
and to determine an impedance morphology curve from said impedance information; characterized in that said medical system comprises
a calculation unit adapted to detect an extreme point section of said impedance morphology
curve and to calculate a measure of a hemodynamic parameter of said heart utilizing
said an extreme point section.
16. The system according to claim 15, wherein said extreme point section is a peak section.
17. The system according to claim 15 or 16, wherein said external programmer apparatus
further comprises an analyzer adapted to analyze said measure to optimize at least
one pacing parameter of said pulse generator or to derive a change of a condition
of said patient, said external apparatus being adapted to communicate said at least
one pacing parameter to said implantable device.
18. The system according to claim 15 or 16, wherein said external programmer apparatus
is adapted to communicate said measure to said implantable device and wherein said
implantable medical device further comprises an analyzer adapted to analyze said measure
to optimize at least one pacing parameter of said pulse generator or to derive a change
of a condition of said patient.
19. The system according to claim 17, or 18, wherein said calculation unit is adapted
to calculate said measure by means of the shape of the impedance morphology curve
in a time window surrounding said peak section of said impedance morphology curve.
20. The system according to any one of preceding claims 15-19, wherein said impedance
morphology determining unit is adapted to determine an averaged impedance morphology
curve from said impedance information during a time interval of a plurality of cardiac
cycles of said heart.
21. The system according to any one of claims 15-20, wherein said impedance morphology
determining unit is adapted to perform a filtering procedure of said received impedance
information and to determine an impedance morphology curve from said filtered impedance
information.
22. The system according to any one of preceding claims 15-21, wherein said calculation
unit is adapted to detect the maximum value of said impedance morphology curve and
to centre said time window about said value.
23. The system according to any one of preceding claims 15-22, wherein said calculation
unit is adapted to fit a polynomial of degree two to the section of the impedance
morphology curve in said time window.
24. The system according to claim 23, wherein said calculation unit is adapted to calculate
a curvature component of said polynomial as said measure.
25. The system according to claim 22, wherein said calculation unit is adapted to:
identify the sample corresponding to the maximum value;
define a window centred about the maximum value containing a predetermined number
of samples;
identify the values of the start and end values of said window, respectively;
calculate an average value of said start and end values; and
calculate a ratio of said average value and said maximum value as said measure.
26. The system according to claim 22, wherein said calculation unit is adapted to
identify the sample corresponding to the maximum value;
define a window centred about the maximum value containing a predetermined number
of samples; and
calculating an area of said window by adding the values of said predetermined number
of samples as said measure.
27. The system according to claim 22, wherein said calculation unit is adapted to
identify the sample corresponding to the maximum value;
define a time window centred about the maximum value containing a predetermined number
of samples;
identify the values of the start and end values of said window, respectively
calculate a first average slope from the sample corresponding to said start value
to said sample corresponding to said maximum value;
calculate a second average slope from the sample corresponding to the maximum value
to the sample corresponding to the end value; and
calculate said measure using said first slope and said second slope.
28. The system according to claim 22, wherein said calculation unit is adapted to
define a time window at a predetermined amplitude in relation to the maximum value;
and
calculating a width of said time window as said measure.
29. The system according to any one of preceding claims 15-28, wherein said hemodynamic
parameter is stroke volume, cardiac output, or contractility.
30. A medical system including an external programmer apparatus comprising a communication
unit and an implantable medical device including a pulse generator adapted to produce
cardiac stimulating pacing pulses, said implantable device being connectable to at
least one lead comprising electrodes for delivering said pulses to cardiac tissue
of a heart of a patient, and a communication unit, said external apparatus and said
implantable device being adapted for two-way communication of data using said communication
units,
wherein said implantable medical device further comprises an impedance measuring unit
connectable to at least two electrodes adapted to measure cardiac impedance of said
heart, said impedance measuring unit being adapted to provide impedance information
corresponding to said measured impedance; and
an impedance morphology determining unit adapted to receive said impedance information
and to determine an impedance morphology curve from said impedance information; and
wherein said external apparatus is adapted to obtain said impedance morphology curve
via said communication unit; characterized in that said medical system comprises
a calculation unit adapted to detect an extreme point section of said impedance morphology
curve and to calculate a measure of a hemodynamic parameter of said heart utilizing
said an extreme point section.
1. Implantierbare medizinische Vorrichtung, die einen Impulsgenerator aufweist, der angepasst
ist, Herzstimulationserregungsimpulse zu erzeugen, wobei die Vorrichtung mit mindestens
einer Leitung verbunden werden kann, die Elektroden zum Abgeben der Impulse an Herzgewebe
eines Herzes eines Patienten umfasst, umfassend:
eine Impedanzmesseinheit, die mit mindestens zwei Elektroden verbunden werden kann
und angepasst ist, die kardiale Impedanz des Herzes zu messen, wobei die Impedanzmesseinheit
angepasst ist, Impedanzinformationen, die der gemessenen Impedanz entsprechen, bereitzustellen,
eine Impedanzmorphologie-Bestimmungseinheit, die angepasst ist, die Impedanzinformationen
zu empfangen und eine Impedanzmorphologiekurve anhand der Impedanzinformationen zu
bestimmen, dadurch gekennzeichnet, dass die medizinische Vorrichtung Folgendes umfasst:
eine Berechnungseinheit, die angepasst ist, einen Extremwertabschnitt der Impedanzmorphologiekurve
zu erkennen und ein Maß eines hämodynamischen Parameters des Herzes unter Verwendung
des einen Extremwertabschnitts zu berechnen.
2. Implantierbare medizinische Vorrichtung nach Anspruch 1, wobei der Extremwertabschnitt
ein Höchstwertabschnitt ist.
3. Implantierbare medizinische Vorrichtung nach Anspruch 1 oder 2, ferner umfassend einen
Analysator, der angepasst ist, das Maß zu analysieren, um mindestens einen Erregungsparameter
des Impulsgenerators zu optimieren oder eine Änderung eines Zustands des Patienten
abzuleiten.
4. Implantierbare medizinische Vorrichtung nach Anspruch 2 oder 3, wobei die Berechnungseinheit
angepasst ist, das Maß mittels der Form der Impedanzmorphologiekurve in einem Zeitfenster,
das den Höchstwertabschnitt der Impedanzmorphologiekurve umgibt, zu berechnen.
5. Implantierbare medizinische Vorrichtung nach einem der vorhergehenden Ansprüche, wobei
die Impedanzmorphologie-Bestimmungseinheit angepasst ist, anhand der Impedanzinformationen
während eines Zeitintervalls mehrerer Herzzyklen des Herzes eine gemittelte Impedanzmorphologiekurve
zu bestimmen.
6. Implantierbare medizinische Vorrichtung nach einem der Ansprüche 1 bis 4, wobei die
Impedanzmorphologie-Bestimmungseinheit angepasst ist, die empfangenen Impedanzinformationen
einem Filtervorgang zu unterziehen und anhand der gefilterten Impedanzinformationen
eine Impedanzmorphologiekurve zu bestimmen.
7. Implantierbare medizinische Vorrichtung nach einem der vorhergehenden Ansprüche, wobei
die Berechnungseinheit angepasst ist, den Maximalwert der Impedanzmorphologiekurve
zu erkennen und das Zeitfenster um den Wert herum zu zentrieren.
8. Implantierbare medizinische Vorrichtung nach einem der vorhergehenden Ansprüche, wobei
die Berechnungseinheit angepasst ist, ein Polynom des Grades 2 an den Abschnitt der
Impedanzmorphologiekurve in dem Zeitfenster anzupassen.
9. Implantierbare medizinische Vorrichtung nach Anspruch 8, wobei die Berechnungseinheit
angepasst ist, eine Krümmungskomponente des Polynoms als das Maß zu berechnen.
10. Implantierbare medizinische Vorrichtung nach Anspruch 7, wobei die Berechnungseinheit
angepasst ist:
den Abtastwert zu erkennen, der dem Maximalwert entspricht;
ein Fenster, das um den Maximalwert herum zentriert ist, zu definieren, das eine festgelegte
Zahl von Abtastwerten enthält;
die Werte der Anfangs- beziehungsweise Endabtastwerte des Fensters zu erkennen;
einen Durchschnittswert aus dem Anfangs- und Endwert zu berechnen, und
ein Verhältnis aus dem Durchschnittswert und dem Maximalwert als das Maß zu berechnen.
11. Implantierbare medizinische Vorrichtung nach Anspruch 7, wobei die Berechnungseinheit
angepasst ist,
den Abtastwert zu erkennen, der dem Maximalwert entspricht;
ein Fenster, das um den Maximalwert herum zentriert ist, zu definieren, das eine festgelegte
Zahl von Abtastwerten enthält; und
eine Fläche des Fensters durch Addieren der Werte der festgelegten Zahl von Abtastwerten
als das Maß zu berechnen.
12. Implantierbare medizinische Vorrichtung nach Anspruch 7, wobei die Berechnungseinheit
angepasst ist,
den Abtastwert zu erkennen, der dem Maximalwert entspricht;
ein Zeitfenster, das um den Maximalwert herum zentriert ist, zu definieren, das eine
festgelegte Zahl von Abtastwerten enthält;
die Werte des Anfangs- beziehungsweise Endwerts des Fensters zu erkennen;
eine erste Durchschnittsneigung von dem Abtastwert, der dem Anfangswert entspricht,
auf den Abtastwert, der dem Maximalwert entspricht, zu berechnen;
eine zweite Durchschnittsneigung von dem Abtastwert, der dem Maximalwert entspricht,
auf den Abtastwert, der dem Endwert entspricht, zu berechnen; und
ein Verhältnis zwischen der ersten Neigung und der zweiten Neigung als das Maß zu
berechnen.
13. Implantierbare medizinische Vorrichtung nach Anspruch 7, wobei die Berechnungseinheit
angepasst ist,
ein Zeitfenster bei einer festgelegten Amplitude bezogen auf den Maximalwert zu definieren,
und
eine Breite des Zeitfensters als das Maß zu berechnen.
14. Implantierbare medizinische Vorrichtung nach einem der vorhergehenden Ansprüche, wobei
der hämodynamische Parameter Schlagvolumen, Herzminutenvolumen oder Kontraktionsfähigkeit
ist.
15. Medizinisches System, das ein externes Programmiergerät, das eine Kommunikationseinheit
umfasst, und eine implantierbare medizinische Vorrichtung aufweist, die einen Impulsgenerator,
der angepasst ist, Herzstimulationserregungsimpulse zu erzeugen, wobei die implantierbare
Vorrichtung mit mindestens einer Leitung verbunden werden kann, die Elektroden zum
Abgeben der Impulse an Herzgewebe eines Herzes eines Patienten umfasst, und eine Kommunikationseinheit
aufweist, wobei das externe Gerät und die implantierbare Vorrichtung für eine Zweiwege-Datenkommunikation
unter Verwendung der Kommunikationseinheiten angepasst sind,
wobei die implantierbare medizinische Vorrichtung ferner eine Impedanzmesseinheit
umfasst, die mit mindestens zwei Elektroden verbunden werden kann und angepasst ist,
die kardiale Impedanz des Herzes zu messen, wobei die Impedanzmesseinheit angepasst
ist, Impedanzinformationen, die der gemessenen Impedanz entsprechen, bereitzustellen,
und
wobei das externe Gerät angepasst ist, die Impedanzinformationen über die Kommunikationseinheit
zu erhalten und ferner Folgendes umfasst
eine Impedanzmorphologie-Bestimmungseinheit, die angepasst ist, die Impedanzinformationen
zu empfangen und eine Impedanzmorphologiekurve anhand der Impedanzinformationen zu
bestimmen,
dadurch gekennzeichnet, dass das medizinische System Folgendes umfasst:
eine Berechnungseinheit, die angepasst ist, einen Extremwertabschnitt der Impedanzmorphologiekurve
zu erkennen und ein Maß eines hämodynamischen Parameters des Herzes unter Verwendung
des einen Extremwertabschnitts zu berechnen.
16. System nach Anspruch 15, wobei der Extremwertabschnitt ein Höchstwertabschnitt ist.
17. System nach Anspruch 15 oder 16, wobei das externe Programmiergerät ferner einen Analysator
umfasst, der angepasst ist, das Maß zu analysieren, um mindestens einen Erregungsparameter
des Impulsgenerators zu optimieren oder eine Änderung eines Zustands des Patienten
abzuleiten, wobei das externe Gerät angepasst ist, den mindestens einen Erregungsparameter
an die implantierbare Vorrichtung zu übertragen.
18. System nach Anspruch 15 oder 16, wobei das externe Programmiergerät angepasst ist,
das Maß an die implantierbare Vorrichtung zu übertragen, und wobei die implantierbare
medizinische Vorrichtung ferner einen Analysator umfasst, der angepasst ist, das Maß
zu analysieren, um mindestens einen Erregungsparameter des Impulsgenerators zu optimieren
oder eine Änderung eines Zustands des Patienten abzuleiten.
19. System nach Anspruch 17 oder 18, wobei die Berechnungseinheit angepasst ist, das Maß
mittels der Form der Impedanzmorphologiekurve in einem Zeitfenster, das den Höchstwertabschnitt
der Impedanzmorphologiekurve umgibt, zu berechnen.
20. System nach einem der vorhergehenden Ansprüche 15 bis 19, wobei die Impedanzmorphologie-Bestimmungseinheit
angepasst ist, anhand der Impedanzinformationen während eines Zeitintervalls mehrerer
Herzzyklen des Herzes eine gemittelte Impedanzmorphologiekurve zu bestimmen.
21. System nach einem der Ansprüche 15 bis 20, wobei die Impedanzmorphologie-Bestimmungseinheit
angepasst ist, die empfangenen Impedanzinformationen einem Filtervorgang zu unterziehen
und anhand der gefilterten Impedanzinformationen eine Impedanzmorphologiekurve zu
bestimmen.
22. System nach einem der vorhergehenden Ansprüche 15 bis 21, wobei die Berechnungseinheit
angepasst ist, den Maximalwert der Impedanzmorphologiekurve zu erkennen und das Zeitfenster
um den Wert herum zu zentrieren.
23. System nach einem der vorhergehenden Ansprüche 15 bis 22, wobei die Berechnungseinheit
angepasst ist, ein Polynom des Grades 2 an den Abschnitt der Impedanzmorphologiekurve
in dem Zeitfenster anzupassen.
24. System nach Anspruch 23, wobei die Berechnungseinheit angepasst ist, eine Krümmungskomponente
des Polynoms als das Maß zu berechnen.
25. System nach Anspruch 22, wobei die Berechnungseinheit angepasst ist:
den Abtastwert zu erkennen, der dem Maximalwert entspricht;
ein Fenster, das um den Maximalwert herum zentriert ist, zu definieren, das eine festgelegte
Zahl von Abtastwerten enthält;
die Werte des Anfangs- beziehungsweise Endwerts des Fensters zu erkennen;
einen Durchschnittswert aus dem Anfangs- und Endwert zu berechnen, und
ein Verhältnis aus dem Durchschnittswert und dem Maximalwert als das Maß zu berechnen.
26. System nach Anspruch 22, wobei die Berechnungseinheit angepasst ist,
den Abtastwert zu erkennen, der dem Maximalwert entspricht;
ein Fenster, das um den Maximalwert herum zentriert ist, zu definieren, das eine festgelegte
Zahl von Abtastwerten enthält; und
eine Fläche des Fensters durch Addieren der Werte der festgelegten Zahl von Abtastwerten
als das Maß zu berechnen.
27. System nach Anspruch 22, wobei die Berechnungseinheit angepasst ist,
den Abtastwert zu erkennen, der dem Maximalwert entspricht;
ein Zeitfenster, das um den Maximalwert herum zentriert ist, zu definieren, das eine
festgelegte Zahl von Abtastwerten enthält;
die Werte des Anfangs- beziehungsweise Endwerts des Fensters zu erkennen;
eine erste Durchschnittsneigung von dem Abtastwert, der dem Anfangswert entspricht,
auf den Abtastwert, der dem Maximalwert entspricht, zu berechnen;
eine zweite Durchschnittsneigung von dem Abtastwert, der dem Maximalwert entspricht,
auf den Abtastwert, der dem Endwert entspricht, zu berechnen; und
das Maß unter Verwendung der ersten Neigung und der zweiten Neigung zu berechnen.
28. System nach Anspruch 22, wobei die Berechnungseinheit angepasst ist,
ein Zeitfenster bei einer festgelegten Amplitude bezogen auf den Maximalwert zu definieren,
und
eine Breite des Zeitfensters als das Maß zu berechnen.
29. System nach einem der vorhergehenden Ansprüche 15 bis 28, wobei der hämodynamische
Parameter Schlagvolumen, Herzminutenvolumen oder Kontraktionsfähigkeit ist.
30. Medizinisches System, das ein externes Programmiergerät, das eine Kommunikationseinheit
umfasst, und eine implantierbare medizinische Vorrichtung aufweist, die einen Impulsgenerator,
der angepasst ist, Herzstimulationserregungsimpulse zu erzeugen, wobei die implantierbare
Vorrichtung mit mindestens einer Leitung verbunden werden kann, die Elektroden zum
Abgeben der Impulse an Herzgewebe eines Herzes eines Patienten umfasst, und eine Kommunikationseinheit
aufweist, wobei das externe Gerät und die implantierbare Vorrichtung für eine Zweiwege-Datenkommunikation
unter Verwendung der Kommunikationseinheiten angepasst sind,
wobei die implantierbare medizinische Vorrichtung ferner eine Impedanzmesseinheit
umfasst, die mit mindestens zwei Elektroden verbunden werden kann und angepasst ist,
die kardiale Impedanz des Herzes zu messen, wobei die Impedanzmesseinheit angepasst
ist, Impedanzinformationen, die der gemessenen Impedanz entsprechen, bereitzustellen,
und
eine Impedanzmorphologie-Bestimmungseinheit, die angepasst ist, die Impedanzinformationen
zu empfangen und eine Impedanzmorphologiekurve anhand der Impedanzinformationen zu
bestimmen, und
wobei das externe Gerät angepasst ist, die Impedanzmorphologiekurve über die Kommunikationseinheit
zu erhalten,
dadurch gekennzeichnet, dass das medizinische System Folgendes umfasst:
eine Berechnungseinheit, die angepasst ist, einen Extremwertabschnitt der Impedanzmorphologiekurve
zu erkennen und ein Maß eines hämodynamischen Parameters des Herzes unter Verwendung
des einen Extremwertabschnitts zu berechnen.
1. Dispositif médical implantable comprenant un générateur d'impulsions adapté pour produire
des impulsions excitatrices de stimulation cardiaque, ledit dispositif pouvant être
connecté à au moins un conducteur comprenant des électrodes pour délivrer lesdites
impulsions au tissu cardiaque d'un coeur d'un patient, comprenant :
une unité de mesure d'impédance pouvant être connectée à au moins deux électrodes
adaptée pour mesurer l'impédance cardiaque dudit coeur, ladite unité de mesure d'impédance
étant adaptée pour fournir des informations d'impédance correspondant à ladite impédance
mesurée ;
une unité de détermination de morphologie d'impédance adaptée pour recevoir lesdites
informations d'impédance et pour déterminer une courbe de morphologie d'impédance
à partir desdites informations d'impédance ; caractérisé en ce que ledit dispositif médical comprend
une unité de calcul adaptée pour détecter une section de pointe extrême de ladite
courbe de morphologie d'impédance et pour calculer une mesure d'un paramètre hémodynamique
dudit coeur en utilisant ladite section de pointe extrême.
2. Dispositif médical implantable selon la revendication 1, dans lequel ladite section
de pointe extrême est une section de pic.
3. Dispositif médical implantable selon la revendication 1 ou 2, comprenant en outre
un analyseur adapté pour analyser ladite mesure pour optimiser au moins un paramètre
excitateur dudit générateur d'impulsions ou pour déduire un changement d'une affection
dudit patient.
4. Dispositif médical implantable selon la revendication 2 ou 3, dans lequel ladite unité
de calcul est adaptée pour calculer ladite mesure au moyen de la forme de la courbe
de morphologie d'impédance dans une fenêtre temporelle entourant ladite section de
pic de ladite courbe de morphologie d'impédance.
5. Dispositif médical implantable selon l'une quelconque des revendications précédentes,
dans lequel ladite unité de détermination de morphologie d'impédance est adaptée pour
déterminer une courbe de morphologie d'impédance moyenne à partir desdites informations
d'impédance pendant un intervalle de temps d'une pluralité de cycles cardiaques dudit
coeur.
6. Dispositif médical implantable selon l'une quelconque des revendications 1 à 4, dans
lequel ladite unité de détermination de morphologie d'impédance est adaptée pour exécuter
une procédure de filtrage desdites informations d'impédance reçues et pour déterminer
une courbe de morphologie d'impédance à partir desdites informations d'impédance filtrées.
7. Dispositif médical implantable selon l'une quelconque des revendications précédentes,
dans lequel ladite unité de calcul est adaptée pour détecter la valeur maximum de
ladite courbe de morphologie d'impédance et pour centrer ladite fenêtre temporelle
autour de ladite valeur.
8. Dispositif médical implantable selon l'une quelconque des revendications précédentes,
dans lequel ladite unité de calcul est adaptée pour ajuster un polynôme de degré deux
à la section de la courbe de morphologie d'impédance dans ladite fenêtre temporelle.
9. Dispositif médical implantable selon la revendication 8, dans lequel ladite unité
de calcul est adaptée pour calculer une composante de courbure dudit polynôme en tant
que ladite mesure.
10. Dispositif médical implantable selon la revendication 7, dans lequel ladite unité
de calcul est adaptée pour :
identifier l'échantillon correspondant à la valeur maximum ;
définir une fenêtre centrée autour de la valeur maximum contenant un nombre prédéterminé
d'échantillons ;
identifier les valeurs respectivement des échantillons de départ et de fin de ladite
fenêtre ;
calculer une valeur moyenne desdites valeurs de départ et de fin ; et
calculer un rapport de ladite valeur moyenne et ladite valeur maximum en tant que
ladite mesure.
11. Dispositif médical implantable selon la revendication 7, dans lequel ladite unité
de calcul est adaptée pour
identifier l'échantillon correspondant à la valeur maximum ;
définir une fenêtre centrée autour de la valeur maximum contenant un nombre prédéterminé
d'échantillons ; et
calculer une surface de ladite fenêtre en additionnant les valeurs dudit nombre prédéterminé
d'échantillons en tant que ladite mesure.
12. Dispositif médical implantable selon la revendication 7, dans lequel ladite unité
de calcul est adaptée pour
identifier l'échantillon correspondant à la valeur maximum ;
définir une fenêtre temporelle centrée autour de la valeur maximum contenant un nombre
prédéterminé d'échantillons ;
identifier les valeurs respectivement des valeurs de départ et de fin de ladite fenêtre
;
calculer une première pente moyenne de l'échantillon correspondant à ladite valeur
de départ audit échantillon correspondant à ladite valeur maximum ;
calculer une seconde pente moyenne de l'échantillon correspondant à la valeur maximum
à l'échantillon correspondant à la valeur de fin ; et
calculer un rapport entre ladite première pente et ladite seconde pente en tant que
mesure.
13. Dispositif médical implantable selon la revendication 7, dans lequel ladite unité
de calcul est adaptée pour
définir une fenêtre temporelle à une amplitude prédéterminée par rapport à la valeur
maximum ; et
calculer une largeur de ladite fenêtre temporelle en tant que ladite mesure.
14. Dispositif médical implantable selon l'une quelconque des revendications précédentes,
dans lequel ledit paramètre hémodynamique est le volume d'éjection systolique, le
débit cardiaque ou la contractilité.
15. Système médical incluant un appareil programmeur externe comprenant une unité de transmission
et un dispositif médical implantable incluant un générateur d'impulsions adapté pour
produire des impulsions excitatrices de stimulation cardiaque, ledit dispositif implantable
pouvant être connecté à au moins un conducteur comprenant des électrodes pour délivrer
lesdites impulsions au tissu cardiaque d'un coeur d'un patient, et une unité de transmission,
ledit appareil externe et ledit dispositif implantable étant adaptés pour la transmission
bidirectionnelle de données en utilisant lesdites unités de transmission,
dans lequel ledit dispositif médical implantable comprend en outre une unité de mesure
d'impédance pouvant être connectée à au moins deux électrodes adaptée pour mesurer
l'impédance cardiaque dudit coeur, ladite unité de mesure d'impédance étant adaptée
pour fournir des informations d'impédance correspondant à ladite impédance mesurée
; et
dans lequel ledit appareil externe est adapté pour obtenir lesdites informations d'impédance
par le biais de ladite unité de transmission et comprend en outre
une unité de détermination de morphologie d'impédance adaptée pour recevoir lesdites
informations d'impédance et pour déterminer une courbe de morphologie d'impédance
à partir desdites informations d'impédance ; caractérisé en ce que ledit système médical comprend
une unité de calcul adaptée pour détecter une section de pointe extrême de ladite
courbe de morphologie d'impédance et pour calculer une mesure d'un paramètre hémodynamique
dudit coeur en utilisant ladite section de pointe extrême.
16. Système selon la revendication 15, dans lequel ladite section de pointe extrême est
une section de pic.
17. Système selon la revendication 15 ou 16, dans lequel ledit appareil programmeur externe
comprend en outre un analyseur adapté pour analyser ladite mesure pour optimiser au
moins un paramètre excitateur dudit générateur d'impulsions ou pour déduire un changement
d'une affection dudit patient, ledit appareil externe étant adapté pour transmettre
ledit au moins un paramètre excitateur audit dispositif implantable.
18. Système selon la revendication 15 ou 16, dans lequel ledit appareil programmeur externe
est adapté pour transmettre ladite mesure audit dispositif implantable et dans lequel
ledit dispositif médical implantable comprend en outre un analyseur adapté pour analyser
ladite mesure pour optimiser au moins un paramètre excitateur dudit générateur d'impulsions
ou pour déduire un changement d'une affection dudit patient.
19. Système selon la revendication 17 ou 18, dans lequel ladite unité de calcul est adaptée
pour calculer ladite mesure au moyen de la forme de la courbe de morphologie d'impédance
dans une fenêtre temporelle entourant ladite section de pic de ladite courbe de morphologie
d'impédance.
20. Système selon l'une quelconque des revendications précédentes 15 à 19, dans lequel
ladite unité de détermination de morphologie d'impédance est adaptée pour déterminer
une courbe de morphologie d'impédance moyenne à partir desdites informations d'impédance
pendant un intervalle de temps d'une pluralité de cycles cardiaques dudit coeur.
21. Système selon l'une quelconque des revendications 15 à 20, dans lequel ladite unité
de détermination de morphologie d'impédance est adaptée pour exécuter une procédure
de filtrage desdites informations d'impédance reçues et pour déterminer une courbe
de morphologie d'impédance à partir desdites informations d'impédance filtrées.
22. Système selon l'une quelconque des revendications précédentes 15 à 21, dans lequel
ladite unité de calcul est adaptée pour détecter la valeur maximum de ladite courbe
de morphologie d'impédance et pour centrer ladite fenêtre temporelle autour de ladite
valeur.
23. Système selon l'une quelconque des revendications précédentes 15 à 22, dans lequel
ladite unité de calcul est adaptée pour ajuster un polynôme de degré deux à la section
de la courbe de morphologie d'impédance dans ladite fenêtre temporelle.
24. Système selon la revendication 23, dans lequel ladite unité de calcul est adaptée
pour calculer une composante de courbure dudit polynôme en tant que ladite mesure.
25. Système selon la revendication 22, dans lequel ladite unité de calcul est adaptée
pour :
identifier l'échantillon correspondant à la valeur maximum ;
définir une fenêtre centrée autour de la valeur maximum contenant un nombre prédéterminé
d'échantillons ;
identifier les valeurs respectivement des valeurs de départ et de fin de ladite fenêtre
;
calculer une valeur moyenne desdites valeurs de départ et de fin ; et
calculer un rapport de ladite valeur moyenne et ladite valeur maximum en tant que
ladite mesure.
26. Système selon la revendication 22, dans lequel ladite unité de calcul est adaptée
pour
identifier l'échantillon correspondant à la valeur maximum ;
définir une fenêtre centrée autour de la valeur maximum contenant un nombre prédéterminé
d'échantillons ; et
calculer une surface de ladite fenêtre en additionnant les valeurs dudit nombre prédéterminé
d'échantillons en tant que ladite mesure.
27. Système selon la revendication 22, dans lequel ladite unité de calcul est adaptée
pour
identifier l'échantillon correspondant à la valeur maximum ;
définir une fenêtre temporelle centrée autour de la valeur maximum contenant un nombre
prédéterminé d'échantillons ;
identifier les valeurs respectivement des valeurs de départ et de fin de ladite fenêtre,
calculer une première pente moyenne de l'échantillon correspondant à ladite valeur
de départ audit échantillon correspondant à ladite valeur maximum ;
calculer une seconde pente moyenne de l'échantillon correspondant à la valeur maximum
à l'échantillon correspondant à la valeur de fin ; et
calculer ladite mesure en utilisant ladite première pente et ladite seconde pente.
28. Système selon la revendication 22, dans lequel ladite unité de calcul est adaptée
pour
définir une fenêtre temporelle à une amplitude prédéterminée par rapport à la valeur
maximum ; et
calculer une largeur de ladite fenêtre temporelle en tant que ladite mesure.
29. Système selon l'une quelconque des revendications précédentes 15 à 28, dans lequel
ledit paramètre hémodynamique est le volume d'éjection systolique, le débit cardiaque
ou la contractilité.
30. Système médical comprenant un appareil programmeur externe comprenant une unité de
transmission et un dispositif médical implantable comprenant un générateur d'impulsions
adapté pour produire des impulsions excitatrices de stimulation cardiaque, ledit dispositif
implantable pouvant être connecté à au moins un conducteur comprenant des électrodes
pour délivrer lesdites impulsions au tissu cardiaque d'un coeur d'un patient, et une
unité de transmission, ledit appareil externe et ledit dispositif implantable étant
adaptés pour la transmission bidirectionnelle de données en utilisant lesdites unités
de transmission,
dans lequel ledit dispositif médical implantable comprend en outre une unité de mesure
d'impédance pouvant être connectée à au moins deux électrodes adaptée pour mesurer
l'impédance cardiaque dudit coeur, ladite unité de mesure d'impédance étant adaptée
pour fournir des informations d'impédance correspondant à ladite impédance mesurée
; et
une unité de détermination de morphologie d'impédance adaptée pour recevoir lesdites
informations d'impédance et pour déterminer une courbe de morphologie d'impédance
à partir desdites informations d'impédance ; et
dans lequel ledit appareil externe est adapté pour obtenir ladite courbe de morphologie
d'impédance par le biais de ladite unité de transmission ; caractérisé en ce que ledit système médical comprend
une unité de calcul adaptée pour détecter une section de pointe extrême de ladite
courbe de morphologie d'impédance et pour calculer une mesure d'un paramètre hémodynamique
dudit coeur en utilisant ladite section de pointe extrême.